ABSTRACT
S. M. Jordan and E. H. Morgan studied the age dependence of the selectivity of macromolecular absorption. According to A. R. Rees and K. H. Wallace, “it is a usual assumption that the selective transport of proteins across cell plasma membranes is mediated by receptor molecules located in the membranes. The function of such receptors is to bind those molecules for which they have the correct stereospecificity. The binding process is usually saturable and occurs with a high affinity between receptor and proteins. IgA tends to decrease while IgG increases in rat milk during the first 1 or 2 weeks of lactation. IgG2a is the major immunoglobulin of rat milk. IgG2a markedly increases in the serum of the suckling rat during the first 2 weeks of life. After ingestion of immunoglobulins with the milk by the suckling rat, IgG has to escape digestion and to cross the surface mucous layer of the enterocytes to reach the receptors.
